(a) Field of the Invention
The present invention relates to a system for manufacturing a flat panel display, and more particularly, to an apparatus for crystallizing amorphous silicon (a-Si) while a thin film transistor array (TFT-Array) panel is formed
(b) Description of Related Art
Liquid crystal displays (LCDs) are widely used in electronic devices. An LCD includes a pair of display panels, which include field generating electrodes formed thereon, and a liquid crystal layer disposed between the pair of display panels. Orientations of liquid crystal molecules of the liquid crystal layer are controlled by voltages supplied to the field generating electrodes. An image may be displayed by controlling a transmittance of a light passing through the liquid crystal layer according to the orientation of the liquid crystal molecules.
Such an LCD may be manufactured by the following processes: Common electrodes and color filters are formed on an upper display panel, and pixel electrodes and thin film transistors are formed on a lower display panel. An alignment layer for aligning liquid crystal molecules is coated on the upper and lower display panels. An active area is defined in a closed-loop shape on the lower display panel by applying a sealant. A liquid crystal is disposed in the active area. The pair of display panels is assembled in a vacuum state, and the sealant is hardened.
Performance of the thin film transistors formed on the lower display panel is important. To improve the performance of the thin film transistors formed on the lower display panel, it is an important that an a-Si (amorphous silicon) of a semiconductor layer of the thin film transistors is crystallized.
A sequential lateral solidification (SLS) type system using a laser is typically used for crystallizing the a-Si. Such an SLS type system includes a moving unit for moving the lower display panel, and a laser unit for irradiating the a-Si of the lower display panel.
The moving unit includes a frame having a rail, a guider adapted to move along the rail, an air bearing disposed between the rail and the guider, and a stage mounted to the guider and holding the display panel.
The laser unit includes a laser source for generating a laser beam, a control lens for controlling an amount of energy of the laser beam, a convergence lens for converging the controlled laser beam, a mask for selectively passing the converged laser beam, and a reducing lens for reducing the passed laser beam to a predetermined focus so as to irradiate the a-Si with the laser beam.
Accordingly, the laser beam irradiates the a-Si of the lower display panel via the laser source, the control lens, the convergence lens, the mask, and the reducing lens.
At the same time, the stage loading the lower display panel moves in a predetermined manner.
The SLS type system may have following problems.
A phenomenon may occur in which a focus of the laser beam formed between the mask and the reducing lens is shaken due to air currents, for example, generated by a movement of the stage, an air current generated by the air bearing, and/or a natural convection due to heat generated from the mask.
The laser beam passing between the mask and the reducing lens is directly affected by the air currents, and accordingly the focus formed between the mask and the reducing lens may be easily shaken.
In a case that the focus formed between the mask and the reducing lens is shaken, a depth of focus (DOF) of the laser beam irradiating the a-Si may not be maintained at a predetermined DOF, and accordingly a device produced thereby may need to be rejected.
Further more, to precisely define a melted region of the a-Si, a resolution of the lens needs to be increased, and consequently the DOF must be decreased. If the focus formed between the mask and the reducing lens is shaken, it may be difficult that such decreased DOF is maintained,
Therefore, a need exists for a system for reducing air currents in a process for manufacturing a flat panel display.